This invention relates to electrostatography, and more particularly to a flexible coupling for transmitting drive torque to a removably component, of an electrostatographic copier or printer, that may b be installed at one time, but not started up for operation unit a later time.
As disclosed for example in U.S. Pat. No. 2,295,003, it is well known to use flexible drive couplings for transmitting drive torque to a driven machine component. Such a coupling could be used for drive coupling a removable component such as copy sheet handling apparatus or development apparatus in an electrostatographic copier or printer, for example, to the main drive of such copier or printer.
Normally such a machine component is installed at one time, but not started up for operation until a later time, and such installation usually is accomplished in the blind. During such installations, the driver and driven halves of the coupling are also more likely, than not, to be misaligned, for example, rotationally. As a consequence, full engagement of the coupling halves is usually achieved in two different stages, at two different times.
Specifically, when the machine component such as the development apparatus above is being installed, a first stage of such two stage engagement will be to move the driven or load half of the coupling axially into the driver half of the coupling unit such axial motion is stopped. Unfortunately however, because of rotational misalignment, such axial motion-stopping contact may not represent full axial engagement between the coupling halves. As a consequence, a second stage involving some rotation of one of the halves at the later startup time, will be necessary in order to allow the driven half to move axially further into the driver half, thereby achieving full engagement.
Such two-stage, two-time engagement of a coupling have been found to result in undesirable shock loads or torque spikes, as well as, in self-defeating coupling wear of the mounting surfaces of the coupling halves. Torque spikes occur during the second stage because at the alter startup time the driver shaft must rotate, under a torque load, through some angle, before the two halves fully engage or close axially. During such rotation at such startup time, the driver half achieves an angular velocity, before the full load of the driven half is added thereto. As a consequence, the load of the driven component is added as a step function to the torque of the already moving driver shaft. The result is a shock load, that is, a torque transient or torque spike, on the driver shaft.
Such torque spikes usually are also transmitted backwards through the driver half, all the way back to the drive means, where they could undesirably interfere with the performance of other driven components int he machine. In the case of the development apparatus of an electrostatographic copier or printer, for example, such torque spikes can result in mechanical perturbations of the image development components of such copier or printer, and hence in defective or poor quality images.
In addition, self-defeating coupling wear of coupling surfaces occurs because final axial engagement motion between the driver and driven halves of the coupling occurs while torque is being transmitted by the moving driver shaft. Since the normal force on the engaging surfaces of the coupling halves is directly proportional to the torque being transmitted, the higher the torque load, the higher the coupling force must be in order to insure complete engagement. Such a high coupling force occurring before full or complete engagement of the force-transmitting surfaces of the coupling halves will undesirably result in a very high initial pressure on the initial and partial points of contacts of such forces.
As further axial penetration or movement occurs during this second stage of engagement, this torque-inflicted high force will be distributed over more and more of the force-transmitting surfaces until full penetration is achieved. Such high initial pressure results in self-defeating coupling wear of the initial points of contacts on such surfaces by gradually radiusing such points of initial contact, and thereby gradually sloping the surfaces. As such slopes increase, an axial force component that tends to defeat coupling by forcing the coupling halves open, begins to develop, and is experienced each time coupling or closing of the coupling halves is attempted.